Torsionally compliant sprocket for engine balance shaft drive and method of manufacture

Abstract

The present invention relates to a torsionally compliant sprocket system which absorbs crankshaft torsional vibrations and minimizes their transfer to other components in the engine system. In particular, the present invention includes a sprocket formed with an elastomeric member located between hub and rim portions. The hub has splines which cooperatively engage with keyways formed in the rim portion through the elastomeric member. A method of forming the compliant sprocket includes forming the hub and rim portions and injection molding an elastomeric material into a gap between the hub and rim portions. While in the mold, heat is applied to the sprocket assembly. The elastomeric member is thus vulcanized in place, creating a one-piece compliant sprocket.

What is claimed is:  
     
       1. An engine balance shaft drive comprising: 
       an engine crankshaft having a compliant crankshaft sprocket disposed thereon;  
       at least one balance shaft having a balance shaft sprocket disposed thereon;  
       a chain drivingly engaging said crankshaft sprocket and said balance shaft sprocket;  
       said compliant crankshaft sprocket having a hub portion secured to said crankshaft and a rim portion, said hub portion having a plurality of radially extending splines, said rim portion located radially about said hub portion and having an inner surface with keyways positioned and adapted to receive said radially extending splines,  
       a plurality of spaced teeth on an outer periphery of said sprocket rim adapted for engagement with said chain;  
       an elastomeric member disposed between said sprocket hub portion and said sprocket rim portion, said elastomeric member being located between said keyways and said splines to form a compliant member therebetween, said compliant member acting to absorb torsional vibrations from said crankshaft and minimize transmittal of said vibrations through said chain to said balance shaft.  
     
     
       2. The engine balance shaft drive of claim  1  further comprising: 
       a second balance shaft having an associated sprocket disposed thereon and drivingly engaging said chain; and  
       an idler shaft having an idler sprocket disposed thereon and drivingly engaging said chain, said idler sprocket positioned between said crankshaft sprocket and said second balance shaft sprocket along said chain so that said first balance shaft rotates in a first direction and said second balance shaft rotates in a direction opposite that of said first direction.  
     
     
       3. The engine balance shaft drive of claim  1  wherein said sprocket rim portion includes a sleeve portion and a toothed plate portion, said toothed plate portion being offset to one side of said sleeve portion. 
     
     
       4. The engine balance shaft drive of claim  1  wherein said sprocket rim is formed in a single piece. 
     
     
       5. The engine balance shaft drive of claim  1  wherein said keyways contain a plurality of position stops, each of said position stops being adapted to contact an adjacent face of said splines when said sprocket rim portion rotates more than a predetermined amount relative to said hub portion. 
     
     
       6. The engine balance shaft drive of claim  1  wherein said splines contain a plurality of position stops, each of said position stops of said splines adapted to contact an adjacent face of said keyways when said sprocket rim portion rotates more than a predetermined amount relative to said hub portion. 
     
     
       7. The engine balance shaft drive of claim  1  wherein said elastomeric material is inserted between said sprocket rim and said hub portion by injection molding.